I wrote Leatherman once about getting my original Super Tool repaired, instead of replaced. They wrote back that it depends if they have the parts in stock at the time the tool arrives, and there is no telling beforehand. So I'm figuring that they must keep the good parts from older tools sent in for warranty, and use them as they are available.
That being said, I'm also thinking that they unless they are specifically asked to repair, they will replace with a current model.
As to the warranty, Tim Leatherman said in an interview years ago that he picked "25 years", because "lifetime" was so overused, and that they have no intention of ever turning away a warranty claim of a long time customer.